“The body makes chemicals that are morphine-like, and when you inject [an opioid], it attaches to the same receptor sites in the brain that would be responsive to the chemicals your body makes that are like morphine,” said Daniel Sitar, professor emeritus in the faculty of health sciences at the University of Manitoba.

“The effect that you get depends on how fast this chemical gets into the brain and how much gets into the brain in a short period of time.”

Fentanyl gets a high amount of chemical into the brain quickly.

Fast-acting opioids like fentanyl affect opioid receptors in areas that control breathing.

Once it’s there, the drug starts attaching to opioid receptors. This kills pain and makes the user feel more calm and less anxious.

Opioids like codeine and morphine do this at a much slower rate, so the primary effects are pain relief and reduced anxiety.

But, Sitar said, with fast-acting opioids like fentanyl, there are other side effects.

For one, the drug makes it easier for the brain to release dopamine, which is associated with reward and pleasure.

“The reason people use it is to get that pleasurable sensation and that reduction of anxiety,” said Sitar. “It gives a pleasurable sensation that is actually a side-effect of the original intent of the drug for medical purposes. Most people enjoy that effect.”

But recreational users also risk lethal side effects.

There are opioid receptors in areas that control breathing.

“The receptors in an area of the brain called the brain stem are actually inhibitory to breathing. So if you have a lot of chemical in the area that controls breathing — mainly the brain stem — it can shut off your body’s normal reflex to breathe,” said Sitar. “The breathing can stop even in a person who is conscious.”

Sitar points to work he did during a clinical study of fentanyl in the 1980s. Researchers were looking at pain management in different age groups.

“We gave fentanyl by blood vessel, and we did it in the operating room because most of them receiving a therapeutic dose of fentanyl stopped breathing about 30 seconds into the dose administration,” said Sitar.

Sitar said the drug’s most lethal effects have to do with breathing. The person will lose consciousness, and — without intervention — they will die.

“We had to talk to them to remind them to breathe,” Sitar said about the subjects of the study.

Watch the video at the top of the story for a visual explanation of how fentanyl kills.